dumpgenerator: Added autoconfirm option

* Added an option that automatically answers 'yes' or 'no' (based on
  user-specified value) to all questions asked by the script.

Signed-off-by: mr.Shu <mr@shu.io>

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This feature is especially useful when using dumpgenerator in some kind of a script that continually dumps wikis. Please also note that it does not break any backwards compatibility.